Semiconductor light-emitting device

ABSTRACT

A II-VI group compound semiconductor light-emitting device can emit light of a short wavelength at room temperature. Operation characteristics, such as current--voltage characteristics and current--light output characteristics can be stabilized and a life of this semiconductor light-emitting device can be extended. The semiconductor light-emitting device comprises a substrate (1), at least a first cladding layer (2) of a first conductivity type, an active layer (3) and a second cladding layer (4) of a second conductivity type, wherein at least the active layer (3) is made of a II-VI group compound semiconductor and the active layer (3) is doped by either or both of n-type and p-type dopants.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor light-emitting device,e.g., a laser diode or light-emitting diode formed of II-VI groupcompound semiconductor, for example.

In order to record and/or reproduce an optical disk and amagneto-optical disk at high density with high resolution, there is anincreasing demand for a green or blue semiconductor laser which can emitgreen or blue light of a short wavelength.

Japan Journal of Applied Physics Vol.31 (1992) pp. L340 to L342described a semiconductor laser having a DH (double hetero) structurecomposed of a ZnSe active layer and a ZnMgSSe cladding layer can bephoto-excited to oscillate at room temperature. An oscillationwavelength of the semiconductor laser having the ZnSe active layer was475.0 nm.

Further, Japan Journal of Applied Physics Vol.33 (1994), pp. L938 toL940 described a semiconductor laser having a SCH (separate confinementheterostructure) composed of a ZnCdSe active layer, a ZnSSe guide layerand a ZnMgSSe cladding layer.

In the above-mentioned two semiconductor lasers, the active layersthereof are not doped.

In the II-VI group compound semiconductor light-emitting device composedof at least one kind of II-group elements, such as Zn, Hg, Cd, Mg or Beand one kind of VI-group elements, such as S, Se or Te, manynon-radiative recombination centers exist on the active layer which isthe light-emitting layer, thereby causing a current--light outputcharacteristic and a current--voltage characteristic to be lowered. As aresult, the semiconductor light-emitting device becomes unreliable.

As factors that act as the non-radiative recombination centers, thereare enumerated dislocations such as a misfit dislocation or a threadingdislocation, a stacking fault, a point defect and a cluster thereof,each of which has a dangling bond.

A degradation nucleus of the above semiconductor light-emitting devicecauses the non-radiative portion to be enhanced through a so-callednon-radiative recombination enhanced defect motion (referred tohereinafter as NRREDM). There is then the problem that the operationcharacteristic is lowered. In particular, if the point defect existswith high density or the point defect forms a cluster, then the pointdefect tends to act as a degradation nucleus. Further, the point defectnot only acts as the degradation nucleus but also moves due to NRREDM,i.e., assumes the degradation process. Therefore, the point defect playsa very important role in degradation of the semiconductor light-emittingdevice.

Of the aforesaid degradation nuclei, the dislocation such as misfitdislocation and threading dislocation and the stacking fault which aregiant defects can be improved based on a substrate used, a substratetreatment, a semiconductor layer structure and a crystal growthcondition, i.e., they are external causes. However, the point defectoccurs based on the crystal growth condition or the like as an externalcause but the point defect intrinsically exists in order to lower a freeenergy based on thermodynamics. These point defects are difficult to bereduced. At the same time, the deterioration caused by these pointdefects has to be suppressed.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a II-VIgroup compound semiconductor light-emitting device which can emit lightof a short wavelength at room temperature.

It is another object of the present invention to provided a II-VI groupcompound semiconductor light-emitting device in which operationcharacteristics, such as current--voltage characteristics andcurrent--light output characteristics can be stabilized.

It is a further object of the present invention to provide a II-VI groupcompound semiconductor light-emitting device whose life can be extended.

According to an aspect of the present invention, there is provided asemiconductor light-emitting device which is comprised of a substrate,at least a first cladding layer of a first conductivity type, an activelayer, and a second cladding layer of a second conductivity type, thefirst cladding layer, the active layer and the second cladding layerbeing formed on the substrate, wherein at least the active layer isformed of a II--VI group compound semiconductor and the active layer isdoped by at least one of n-type and p-type dopants.

According to another aspect of the present invention, there is provideda semiconductor light-emitting device which oscillates at roomtemperature. This semiconductor light-emitting device is comprised of asubstrate, at least a first cladding layer of a first conductivity type,an active layer, and a second cladding layer of a second conductivitytype, wherein the active layer is made of ZnSe, the first and secondcladding layers are made of ZnMgSSe and the active layer is doped by Cl.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a semiconductorlight-emitting device according to a first embodiment of the presentinvention;

FIG. 2 is a schematic diagram showing an example of a molecular beamepitaxy apparatus used in the present invention;

FIG. 3 is a characteristic graph showing a relationship between band gapand hole concentration;

FIG. 4 is a spectrum diagram showing measured results of light emittedfrom the semiconductor light-emitting device according to the presentinvention;

FIG. 5 is a graph showing an impurity concentration dependence relativeto a PL (photoluminescence) light-emission intensity and which is usedto explain the present invention;

FIG. 6 is a graph showing an impurity concentration dependence of ahalf-amplitude level relative to a PL light-emitting spectrum and whichis used to explain the present invention;

FIG. 7 is a schematic cross-sectional view showing a semiconductorlight-emitting device according to a second embodiment of the presentinvention;

FIG. 8 is a characteristic graph showing measured results of operationcurrents--voltage characteristics of the inventive semiconductorlight-emitting device and the conventional semiconductor light-emittingdevice;

FIG. 9 is an energy band diagram used to explain the semiconductorlight-emitting device according to the present invention; and

FIG. 10 is a schematic cross-sectional view showing a semiconductorlight-emitting device according to a third embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A semiconductor light-emitting device according to a first embodiment ofthe present invention will hereinafter be described with reference toFIG. 1.

According to this embodiment, as shown in FIG. 1, a II-VI group compoundsemiconductor, e.g., semiconductor laser is formed on a GaAs substrate 1by epitaxially growing a ZnMgSSe II-VI group compound semiconductorlayer.

Semiconductor layers were epitaxially grown on the substrate 1 by a MBE(molecular beam epitaxy) apparatus. FIG. 2 shows a schematic arrangementof the MBE apparatus. The MBE apparatus is a kind of vacuum depositionapparatus and includes a vacuum chamber 41 having a ultra-high vacuumexhausting apparatus (not shown). In this chamber 41, there is disposeda substrate holder 42 for holding a substrate 1 on which a II-VI groupcompound semiconductor is formed.

Within the chamber 41, there are disposed a plurality of molecular beamsources (K cells) 43 in an opposing relation to the substrate 1. Themolecular beam sources 43 are material sources for the II-VI groupcompound semiconductor. The chamber 41 includes a plasma generatingchamber 44 which radiates plasma N (nitrogen) to the substrate 1. Thisplasma generating chamber 44 is of an ECR (electron cyclotron resonance)cell arrangement. The plasma generating chamber 44 includes a magnet 45,a microwave terminal 46 for supplying microwaves and a nitrogen gasintroducing tube 47 for supplying a nitrogen gas.

According to this MBE apparatus, a II-VI group compound semiconductor isepitaxially grown on the substrate 1 by radiation of molecular beamsfrom the II-VI group compound semiconductor material molecular beamsource of the molecular beam source 43 to the substrate 1.

When a nitrogen-doped p-type II-VI group compound semiconductor isepitaxially grown on the substrate 1, a nitrogen gas is generated asplasma nitrogen N according to the ECR (electron cyclotron resonance)energized on application of a magnetic field and a microwave in theplasma generating apparatus 44. The plasma nitrogen N is introducedthrough a plasma introducing inlet 48 into the plasma generating chamber44 to radiate the substrate 1 together with radiation of molecularbeams. Then, the nitrogen-doped, i.e., p-type II-VI group compoundsemiconductor can be epitaxially grown by radiating the substrate 1 withmolecular beams from the molecular beam source 43.

When a Cl-doped n-type II-VI group compound semiconductor is epitaxiallygrown on the substrate 1, a Cl-doped n-type II-VI group compoundsemiconductor can be epitaxially grown on the substrate 1 by radiationof molecular beams from the II-VI group compound semiconductor materialmolecular beam source of the molecular beam source 43 and from the Clmolecular beam source to the substrate 1.

The semiconductor light-emitting device shown in FIG. 1 is formed byusing this epitaxial growth apparatus. In this case, as shown in FIG. 1,on a first conductivity type, e.g., n-type GaAs substrate 1, there isepitaxially grown a ZnSe buffer layer 5 on which there are epitaxiallygrown a first cladding layer 2 having a thickness of about 1 μm of afirst conductivity type made of ZnMgSSe doped by Cl as n-type impurity,a ZnSe active layer 3 having a thickness of about 70 nm and a secondcladding layer 4 having a thickness of about 1 μm of a secondconductivity type, in this embodiment, ZnMgSSSe doped by N (nitrogen) ofp-type impurity, in that order.

On the second cladding layer 4, there are grown respective layers tomake a satisfactory ohmic-contact with a p-side electrode by continuousepitaxy. A first semiconductor layer 6 having a thickness of about 200nm made of ZnSSe doped by N of first conductivity type, i.e., p-typeimpurity, a second semiconductor layer 7 having a thickness of about 700nm made of ZnSe, a superlattice structure semiconductor layer 8 in whichN-doped ZnTe and ZnSe are alternately laminated and a contact layer 9made of N-doped ZnTe are epitaxially grown on the second cladding layer4, in that order.

On the contact layer 9, there is deposited an insulating layer 10 ofpolyimide or the like, An opening 10W is bored on a current path portionof a stripe-shaped pattern extending in the direction perpendicular tothe sheet of drawing of FIG. 1 by a suitable process, such asphotolithography. Thereafter, a p-side electrode 11 having a laminatedstructure in which Pd having a thickness of about 10 nm, Pt having athickness of 100 nm and Au having a thickness of 300 nm are deposited onthe whole surface from the contact layer 9 side is formed on the contactlayer 9 through the opening 10W of the insulating layer 10 so as to makean ohmic contact.

Further, an electrode 12 such as In is deposited on the rear surfaceside of the substrate 1, thereby a semiconductor light-emitting device,e.g., semiconductor laser being formed.

The active layer 3 is doped by either or both of n-type and p-typedopants, i.e., impurity. A concentration of dopant in the active layer 3is selected to be 1×10¹⁵ /cm⁻³ or greater. At that time, a point defectdensity can be controlled and a degradation velocity can be controlledso that the life of the semiconductor light-emitting device can beextended.

The active layer 3 is made of ZnSe, for example, and doped by Cl with adopant atomic concentration of 1×10¹⁵ to 5×10¹⁶ cm⁻³ as n-type dopant.As a Cl doping material, there can be used ZnCl₂ serving as Cl impuritysource of one of the molecular beam sources 43 shown in FIG. 2.

A bandgap energy (at 77K) Eg of the cladding layer, in particular, thep-type cladding layer 4 is selected so as to satisfy Eg=3.0 eV±0.05 eV.FIG. 3 shows a relationship between a bandgap energy Eg and a holeconcentration N_(p) (cm⁻³) obtained in Japanese patent application No.5-288653 proposed by the same assignee of this application under thetitle of "Semiconductor Laser". In FIG. 3, reference letter T denotes asemiconductor laser operation temperature (K) k denotes a Boltzmannconstant (eV/K). Study of FIG. 3 reveals that the bandgap energy Eg ofthe p-type cladding layer 4 should preferably be selected so as tosatisfy Eg=3.0 eV±0.05 eV in order to obtain a high hole concentration.

FIG. 4 is a spectrum diagram showing measured results of oscillation ofthe inventive semiconductor laser shown in FIG. 1 wherein the activelayer 3 is made of n-type Cl-doped ZnSe. In that case, the semiconductorlaser emitted laser beam having a wavelength of 471 nm and itshalf-amplitude level presented a narrow and steep oscillation spectrum.A threshold current density was 20 kA/cm².

While the semiconductor laser in which the active layer 3 is made ofZnSe which is not doped by impurity could not emit laser beam at roomtemperature, according to the present invention, the semiconductor laserhaving the ZnSe active layer 3 can emit laser beam having a shortwavelength of 471 nm at room temperature.

FIGS. 5 and 6 show measured results of light-emitting intensity of PL(photoluminescence) based on photo-excitation and half-amplitude levelof PL light-emission spectrum obtained when an atomic concentration(cm⁻³) of dopant in the Cl-doped ZnSe is changed in the PL where ZnSe isepitaxially grown on the GaAs substrate, respectively.

Study of FIGS. 5 and 6 shows that PL intensity can be increased byincreasing the dopant concentration and that the point defect densityand the degradation velocity can be suppressed, accordingly, the life ofthe semiconductor laser can be extended as will be described later on.On the other hand, if the atomic concentration of dopant exceeds 1×10¹⁵cm⁻³, then the half-amplitude level increases. Thus, the Light-emittingoperation current and a threshold current I_(th) tend to increase.However, when the atomic concentration of dopant is selected to be1×10¹⁵ to 5×10¹⁶ cm⁻³, the effect achieved by the increase of PLintensity excels the effect achieved by the increase of half-amplitudelevel. Therefore, the semiconductor laser using the ZnSe active layerbecame able to emit laser beam of a short wavelength at roomtemperature. Moreover, since the light-emitting efficiency can beimproved, it became possible to lower the operation current and thethreshold current.

As described above, when the atomic concentration of the n-type dopantin the active layer was selected to be 1×10¹⁵ to 5×10¹⁶ cm⁻³, thelight-emitting efficiency could be improved and the threshold currentI_(th) could be lowered. The reason that the dopant concentration isselected to be 1×10¹⁵ cm⁻³ or higher is that, if the dopantconcentration is less than 1×10¹⁵ cm⁻³, then the semiconductor laserusing the ZnSe active layer can not emit laser beam at room temperatureand that a light-emitting intensity in a semiconductor laser using aZnCdSe active layer is low. This is because a non-radiative centerincreases when the active layer is not doped by dopant.

While the active layer 3 is doped Cl by as described above, it ispossible to dope the active layer 3 by using ZnCl₂ as a dopant materialwhen the active layer is epitaxially grown, e.g., as one of themolecular beam sources 43 in the MBE apparatus shown in FIG. 2.

Since the active layer can be doped by Cl according to the molecularbeam source based on ZnCl₂, an active layer having an excellentcrystallinity can be epitaxially grown easily as compared with the casethat a dopant is processed as a plasma dopant for doping the activelayer.

While the semiconductor laser has the so-called DH structure wherein theactive layer 3 is directly sandwiched between the first and secondcladding layers 2 and 4 according to the first embodiment shown in FIG.1, the present invention is not limited thereto and can also be appliedto a semiconductor laser of SCH structure in which first and secondguide layers are interposed among an active layer and first and secondcladding layers.

A second embodiment according to the present invention wherein asemiconductor light-emitting device is applied to a semiconductorlight-emitting device having a SCH structure will be described withreference to FIG. 7. In FIG. 7, like parts corresponding to those ofFIG. 1 are marked with the same references.

Also in this embodiment, on the first conductivity type, e.g., n-typeGaAs substrate 1, there are epitaxially grown the ZnSe buffer layer 5,the ZnMgSSe first cladding layer 2 doped by Cl as a first conductivitytype, e.g., n-type impurity, a ZnSSe first guide layer 21 doped by Cl asa first conductivity type, e.g., n-type impurity, the ZnCdSe activelayer 3 doped by Cl as a first conductivity type, e.g., n-type impurity,a ZnSSe second guide layer 22 doped by N (nitrogen) of a secondconductivity type, e.g., n-type impurity and the second cladding layer 4doped by N (nitrogen) of a second conductivity type, in that order.

Subsequently, on the second cladding layer 4, there are epitaxiallycontinuously grown respective layers in order to make a satisfactoryohmic contact. In this embodiment, on the ZnSSe first semiconductorlayer (capping layer) 6 doped by N (nitrogen) as a second conductivitytype, e.g., p-type impurity, there are epitaxially grown thesuperlattice structure semiconductor layer 8 wherein N-doped ZnTe andZnSe are alternately laminated and the contact layer 9 made of N-dopedZnTe or the like, in that order.

In this embodiment, a groove 23 crossing the contact layer 9 and thesuperlattice structure semiconductor layer 9 are formed on the firstsemiconductor layer 6 at both sides of a central stripe portion byselective etching based on photolithography. An Al₂ O₃, for example, isdeposited on the whole surface including the inside of the groove 23from the etching resist used in the selective etching by vapordeposition, for example. Then, Al₂ O₃ in the stripe portion is liftedoff by the removal of the etching resist, whereby the insulating layer10 made of Al₂ O₃ is selectively filled into the groove 23 to form acurrent confinement layer. Moreover, the contact layer 9 of the stripeportion is exposed to the outside.

Thereafter, Pd, Pt or Au, for example, is similarly deposited on thewhole surface of the contact layer 9 side by vapor deposition to therebyform the p-side electrode 11 having the laminated structure to make anohmic-contact with the contact layer 9.

Further, the electrode 12 such as In is also deposited on the rearsurface side of the substrate 1, thereby the semiconductorlight-emitting device, e.g., semiconductor laser being formed.

FIG. 8 shows measured results of operation current characteristicsversus to an operation time obtained when the semiconductor laser devicearranged as shown in FIG. 7 is continuously operated at room temperaturewhere an intensity of light output is 0.1 [mW]. Characteristic curves 81and 82 in FIG. 8 plot measured results of operation currents concerningtwo semiconductor laser devices wherein the active layer 3 is doped byCl with a dopant concentration of 10¹⁷ cm⁻³. Characteristics 83 and 84in FIG. 8 plot similar measured results concerning two semiconductorlaser devices having the SCH structures similar to the structure shownin FIG. 7 and wherein the active layer 3 is not doped by dopant. Havingcompared the inventive semiconductor laser devices and the conventionalsemiconductor laser devices, it is to be understood that thesemiconductor laser device according to the present invention couldimprove the deterioration of characteristics remarkably.

The reason for this is as follows. That is, according to the presentinvention, since the active layer is doped by impurity, a point defectdensity which becomes a non-radiative recombination center can belowered. Further, since the point defect density is lowered and acluster of point defect is suppressed, it is possible to avoid theoccurrence of phenomenon wherein a non-radiative portion is enhancedthrough the NRREDM when the point defect acts as a degradation nucleus.Furthermore, since a slope of a defect density distribution in theactive layer can be made gentle, a diffusion of point defect into theactive layer can be suppressed.

If the concentration of dopant doped in the active layer 3 is selectedto be higher than 1×10¹⁷ cm⁻³, for example, in excess of 1×10¹⁵ cm⁻³,then a vacancy density, i.e., point defect density can be lowered morereliably.

As described above, according to the arrangement of the presentinvention, since the point defect density can be lowered, thenon-radiative recombination caused by this point defect can be lowered,thereby making it possible to improve the operation characteristic suchas the current--light output characteristic an the current--voltagecharacteristic. When the point defects exists with a high density or thepoint defect forms the cluster as described before, the point defecttends to act as the degradation nucleus and moves due to the NRREDM,i.e., undertakes a degradation process. Therefore, since the pointdefect density can be lowered, the degradation of the operationcharacteristics such as light-emitting efficiency, current--light outputcharacteristic and current--voltage characteristic can be avoided, i.e.,the semiconductor light-emitting device can be made more reliable andthe life of the semiconductor light-emitting device can be extended.

The deterioration of the above-mentioned characteristics occursremarkably when the defect formed of the cluster of point defects isenhanced in the active layer from a dislocation of line defect, forexample. The defect tends to increase when a vacancy of II-group atomand a vacancy of VI-group atom exit at the same time in the same number.According to the arrangement of the present invention, if one of chargedvacancy of II-group atom, e.g., Zn and charged vacancy of VI-group atom,e.g., Se increases when a chemical potential is moved by dopingimpurity, then the other decreases. Therefore, the defect is difficultto be enhanced and the characteristics become difficult to be degraded.

Further, according to the above-mentioned arrangement, since theinclination of the point defect distribution in the active layer becomesgentle, the point defect becomes difficult to be diffused into theactive layer to thereby suppress the characteristics of the active layerfrom being degraded much more. FIG. 9 shows a band model in the activelayer and n-type and p-type cladding layers or guide layers obtainedwhen the active layer is doped by the n-type dopant. In this case, sincethe active layer is doped by the n-type dopant, a chemical potential μin this active layer becomes a flat level or gentle slope substantiallythe same as chemical potential of the n-type cladding layer or guidelayer adjoining the active layer with the result that the distributionin the active layer of the point defect (vacancy), i.e., in thedepletion layer becomes flat or gentle. Therefore, the point defectbecomes difficult to be diffused in the active layer.

While the horizontal resonator is arranged such that its resonatorlength direction is extended in the layer surface direction of theactive layer 3 and in the direction (direction perpendicular to thesheets of drawings of FIGS. 1 and 7) along the extended direction of thestripe-shaped electrode 11 in the first and second embodiments shown inFIGS. 1 and 7, as shown in a cross-sectional view of FIG. 10 taken alongthe line X--X in FIG. 7, a coating film 30 having a multi-layerstructure composed of a first film 21 formed of an Al₂ O₃ and a secondfilm 22 formed of a silicon (Si) film is deposited on both end faces,i.e., light-emitting end faces of the horizontal resonator to set areflectivity and a transmittance on the end faces.

While the semiconductor light-emitting device emits light from thehorizontal direction in the embodiments shown in FIGS. 1, 7 and 10, thepresent invention is not limited thereto and the semiconductorlight-emitting device can be formed as a so-called surface emittingstructure wherein the thickness of the electrode 11, for example, isselected to be less than 100 nm and light is emitted in the directionperpendicular to the surface of the active layer 3. Further, in order toimprove the light-emitting efficiency, a Bragg reflector formed of asuperlattice composed of Cl-doped ZnMgSSe thin film and ZnSSe thin filmcan be disposed between the substrate 1 and the first cladding layer 2.At that time, the contact layer 9 composed of the p-type ZnTe and thesuperlattice structure semiconductor layer 8 can be removed.

While the first conductivity type is the n-type and the secondconductivity type is the p-type as described above, the presentinvention is not limited thereto and the first conductivity type may bethe p-type and the second conductivity type may be the n-type. Inaddition, the present invention can be applied to various arrangementsof II-VI group compound semiconductor light-emitting devices.

When the active layer is the ZnSe active layer, the semiconductorlight-emitting device can emit light having a short wavelength, e.g.,471 nm. In addition, the light-emitting efficiency can be improved andthe operation current can be lowered. The active layer can be made ofZnCdS or other II-VI group compounds such as ZnSSe.

The dopant by which the active layer 3 is doped is not limited to anyone of the n-type and p-type dopants but instead the vacancy, i.e.,point defect density can be controlled and densities of vacancies ofII-group atom and VI-group atom can be controlled by doping both then-type and p-type dopants to predetermined densities.

If the n-type dopant for doping the active layer 3 is Cl, then theimpurity can be made the same as the impurity of other n-typesemiconductor layer such as the cladding layer, which is advantageousfrom a productivity standpoint. Since ion radius is smaller than that ofhost, e.g., ZnCdSe, the crystal can be solidified and the increase ofdislocation due to the NRRED can be suppressed effectively. However, thedopant is not limited to the Cl and Ga also can be used.

The dopant for the active layer is not limited to the n-type dopant anda p-type dopant can be used. In particular, if the dopant for the activelayer is the p-type dopant, N (nitrogen) can be doped by plasma doping.Further, the active layer can be doped by both the n-type and p-typedopants.

While the respective semiconductor layers are epitaxially grown on thesubstrate 1 by MBE as described above, the present invention is notlimited thereto and the semiconductor layers can be epitaxially grown onthe substrate 1 by MOCVD (metal organic chemical vapor deposition).

While the electrode 11, for example, is contacted with the contact layer9 in a stripe fashion to construct the semiconductor laser of stripearrangement as described above, the present invention is not limitedthereto and a semiconductor laser having a stripe portion can befabricated by forming a current confinement portion on both sides of thestripe forming portion. Thus, the present invention is not limited tothe above-mentioned arrangement and can be modified variously.

Further, the present invention is not limited to the semiconductor laserand can be applied to a light-emitting diode without resonatorarrangement based on the stripe arrangement.

As described above, according to the II-VI group compound semiconductordevice of the present invention, it is possible to form thesemiconductor light-emitting device having excellent characteristics andwhose life can be extended by doping the active layer 3 with at leastone of n-type and p-type dopants.

If the active layer is made of ZnSe, then it becomes possible to formthe semiconductor light-emitting device which can emit light of a shortwavelength at room temperature. If other active layers, e.g., ZnCdSe andZnSSe active layers are used, then the light-emitting efficiency can beimproved more, the operation current can be lowered and the thresholdcurrent I_(th) can be lowered. Thus, if the semiconductor light-emittingdevice according to the present invention is used as a light source ofan optical recording and reproducing apparatus, then the recording canbe made with high density and high resolution by light having the shortwavelength. Furthermore, the power consumption can be reduced.Therefore, the semiconductor light-emitting device according to thepresent invention can bring various advantages in actual practice.

Having described preferred embodiment of the invention with reference tothe accompanying drawings, it is to be understood that the invention isnot limited to those precise embodiments and that various changes andmodifications could be effected therein by one skilled in the artwithout departing from the spirit or scope of the invention as definedin the appended claims.

What is claimed is:
 1. A semiconductor light-emitting device comprising:a substrate; at least a first cladding layer of a first conductivity type; an active layer; and a second cladding layer of a second conductivity type, said first cladding layer, said active layer and said second cladding layer being formed on said substrate, wherein at least said active layer is formed of a II-VI group compound semiconductor and said active layer contains a dopant at a concentration of greater than 1×10¹⁵ cm⁻³ and less than 5×10¹⁶ cm⁻³.
 2. A semiconductor light-emitting device according to claim 1, wherein said active layer is a ZnSe active layer.
 3. A semiconductor light-emitting device according to claim 1, wherein said active layer is a ZnCdSe active layer.
 4. A semiconductor light-emitting device according to claim 1, wherein said dopant of said active layer is Cl.
 5. A semiconductor light-emitting device according to claim 4, wherein a dope material of said Cl is ZnCl₂.
 6. A semiconductor light-emitting device according to claim 1, wherein said dopant of said active layer is nitrogen.
 7. A semiconductor light-emitting device comprising:a substrate; at least a first cladding layer of a first conductivity type; an active layer; and a second cladding layer of a second conductivity type, wherein said active layer is made of ZnSe, said first and second cladding layers are made of ZnMgSSe and said active layer contains a dopant at a concentration of greater than 1×10¹⁵ cm⁻³ and less than 5×10¹⁶ cm⁻³.
 8. The semiconductor device of claim 7, wherein the dopant of the active layer is Cl and the semiconductor device oscillates at room temperature.
 9. A semiconductor light-emitting device comprising:a substrate; a first cladding layer; a first guide layer on the first cladding layer; an active layer on the first guide layer; a second guide layer on the active layer; a second cladding layer on the second guide layer; and wherein said active layer contains a dopant at a concentration of greater than 1×10¹⁵ cm⁻³ and less than 5×10¹⁶ cm⁻³.
 10. A semiconductor light-emitting device according to claim 1, wherein a concentration of the dopant is greater than 1×10¹⁵ cm⁻³.
 11. A semiconductor light-emitting device according to claim 7, wherein a concentration of the dopant is greater than 1×10¹⁵ cm⁻³.
 12. A semiconductor light-emitting device according to claim 9, wherein a concentration of the dopant is greater than 1×10¹⁵ cm⁻³. 